File photo of traders working on the floor of the New York Stock Exchange shortly after the opening bell in New York Thomson Reuters By Chuck Mikolajczak

NEW YORK (Reuters) - The first few months of the year have given investors both severe selloffs and powerful rallies, and U.S. stocks have now limped into the record books with the second-longest bull market in history - with an asterisk.

The S&P 500 technically peaked on May 21, 2015 at 2,130.82. To validate that the bull lives, the index will have to surpass those levels before it declines 20 percent from there and becomes a bona fide bear market. If that happens, the bull would go down in history as having ended last May as the third longest ever.

Should the S&P surpass its May 2015 levels - it is close now, even after a bad seven days - it will become second only to the extraordinarily prolonged bull of Oct. 1990 to March 2000 in longevity.

The bull market is now 2,608 days old, moving past the postwar party that lasted from June 1949 to Aug. 1956. The average run of the 13 longest bull markets is 1,797 days. During the current run, the index has risen about 210 percent, giving it the fifth best performance among bull markets.

If it gets there, it will have been a rocky ride.

Stocks started 2016 with a historically bad start, as concerns about a recession pushed the index down more than 14 percent on Feb. 11 from its record high set on May 21.

But then the index rallied hard and now stands 1.9 percent off its record.

The question now from here is whether the market can advance notably beyond this point. The index has stalled out over the past seven days, with disappointing earnings from heavyweights in the tech sector such as Apple and Alphabet providing a stiff deterrent to further gains.

Valuations may also be part of what is holding stocks back. The forward price-to-earnings ratio of the S&P stands at 17, its highest level since registering a 17.1 ratio in early June.

"All of our dials are pointing positive with the exception of valuations," said Jack Ablin, chief investment officer at BMO Private Bank in Chicago. To justify the market's current price levels would take a big ramp up in revenues and rebound in earnings, he said. "I'm not sure I see that in the cards."

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